In the recent drive for higher integration and operating speeds in LSI devices, the pattern rule is made drastically finer. The background supporting such a rapid advance is a reduction of wavelength of the light source for exposure. A change-over took place from i-line (365 nm) of a mercury lamp to shorter wavelength KrF excimer laser (248 nm) and then to ArF excimer laser (193 nm). With the ArF excimer laser lithography, efforts are made to enable the fabrication of 65-nm node devices. The current research is made on the ArF immersion lithography in which ArF excimer laser is irradiated through water held between the projection lens and the wafer. A combination of a lens having NA of at least 1.2 with ultra-high resolution technology suggests a way to the 45-nm node (see Proc. SPIE, Vol. 5040, p 724, 2003).
The ArF immersion lithography has a possibility that water-soluble components in the resist film be leached in immersion water during exposure. As a result, the pattern may change its shape or even collapse (known as pattern collapse). It is also pointed out that water droplets remaining on the resist film after scanning, though in a minute volume, can induce defects. It was then proposed to provide a protective film on the resist film to prevent resist components from being leached out and water from causing to form defects, the process being referred to as “topcoat process.” See 2nd Immersion Workshop: Resist and Cover Material Investigation for Immersion Lithography, 2003.
In the ArF immersion lithography using a topcoat, a protective coating material which is soluble in alkaline developer offers great cost and process merits because the protective film can be removed at the same time as development. Thus, great efforts have been devoted to develop water-insoluble resist protective coating materials based on alkali-soluble resins. See WO 2005/42453.
On the other hand, a process for preventing resist components from being leached out in water without a need for a protective coating material has also been developed, the process being referred to as “topcoatless process”. See JP-A 2006-48029 and JP-A 2006-309245. In the topcoatless process, an alkali-soluble hydrophobic polymer is added to the resist material as a surfactant, whereupon the hydrophobic compound is segregated at the resist surface during resist film formation. The process is thus expected to achieve equivalent effects to the use of topcoat. Additionally, the topcoatless process is economically advantageous because steps of forming and removing the protective film are unnecessary.
In either of the topcoat and topcoatless processes, the ArF immersion lithography requires a scanning speed of about 300 to 700 mm/sec in order to gain higher throughputs. Recent efforts are made to further increase the scanning speed. In the event of such high-speed scanning, if the water repellency of the resist or protective film is insufficient, water droplets may be left on the film surface after scanning. Residual droplets may cause defects. To obviate such defects, it is necessary to improve the water repellency and water slip (in terms of receding contact angle) of the relevant coating film.
One known means for improving the water repellency and water slip of a resin is by introducing fluorine atoms into the polymer skeleton. For example, a copolymer of α-trifluoromethyl acrylate and norbornene derivative (Proc. SPIE Vol. 4690, p 18, 2002) and a fluorinated cyclic polymerization polymer having a fluorinated alcohol unit on side chain (Proc. SPIE Vol. 6519, p 651905 (2007)) exhibit good properties of water repellency and water slip. The latter polymer is further improved in water slip by protecting the fluorinated alcohol with acid labile groups.
Although the introduction of fluorine into the polymer skeleton brings remarkable improvements in water repellency and water slip, the introduction of extra fluorine can induce new defects known as “blob defects”. Blob defects are likely to form during spin drying after development, particularly when the film has a high surface contact angle after development. One approach for obviating blob defects is by introducing highly hydrophilic substituent groups (e.g., carboxyl or sulfo groups) into a resin to reduce the surface contact angle after development. However, since these groups serve to noticeably reduce the water repellency and water slip of the resin, this approach is not compatible with high-speed scanning. There is a desire to have a material which can minimize blob defects while maintaining highly water repellent and water slip properties during immersion lithography.
The highly water repellent/water slippery materials discussed above are expected to be applied not only to the ArF immersion lithography, but also to the resist material for mask blanks. Resist materials for mask blanks are subject to long-term exposure in vacuum. It is pointed out that sensitivity variations or profile changes can occur as an amine component in the resist material is adsorbed to the resist film surface during the long-term exposure. It was then proposed to lay a protective film on a resist film for preventing adsorption of amine to the resist film.